1. Field of the Invention
The present invention relates to cooling mediums at elevated temperatures, such as 130.degree. C.
2. Description of the Prior Art
Heat-stabilized, glass-fibre-reinforced polyamide (PA) 66 is successfully used throughout the world in motor vehicle coolant systems. The economical and efficient manufacture of cooling water tanks, water pipes and thermostatic valve housings in addition to high dynamic loading capacity and resistance to the cooling medium at 108.degree. C. predestines PA 66 for this field of application. Development work to increase the efficiency of internal combustion engines expects higher temperature stresses in the cooling medium. Demands on mechanical properties following contact with the cooling medium at 130.degree. C. are increasing.
A mixture comprising ethylene glycol:water in the ratio 1:1 is described as cooling medium in the motor vehicle field. The mixture solidifies at -30.degree. C. and boils at 108.degree. C. Azeotropic distillation is not involved. First of all, the water distils off at 108.degree. C. The temperature of the boiling material increases as the ethylene glycol content increases, until pure glycol distils at 197.4.degree. C.
If the temperature of the cooling medium in the closed cooling system rises to 130.degree. C., the internal pressure rises to 2 bars. With the increase in the operating temperature of the cooling medium, in addition to very good tightness, high mechanical strength values at 130.degree. C. in the state saturated with cooling medium are a prerequisite for the operation of the cooling system. If part of the cooling medium escapes as steam, the ethylene glycol content in the cooling medium increases. Components made of polyamide may partially dissolve if glycol content and temperature increase perceptibly.
The object of the invention was therefore to develop a cooling medium which operates at the desired temperatures (approx. 130.degree. C.) without pressure increase and does not perceptibly impair the mechanical properties of polyamide.
The invention provides a cooling medium containing
A) 35-65, preferably 45 to 55 wt. % of polyethylene glycol PA1 B) 35-65, preferably 45 to 55 wt. % of ethylene glycol.
The cooling medium is suitable for cooling motor vehicle engines.